COLLISION BROADENING OF ROTATIONAL ABSORPTION LINES .V. PRESSURE BROADENING OF MICROWAVE ABSORPTION SPECTRA INVOLVING ASYMMETRIC-TOP MOLECULES

Pressure broadening of microwave absorption spectra by collisions involving asymmetric-top molecules either as absorbing or as perturbing molecules has been investigated within the framework of a pressurebroadening theory presented earlier. Modifications of this theory are required because of the increased mathematical complexity involved in asymmetric-top calculations and because asymmetric-top molecules may have two energy levels spaced relatively close together with all other levels widely spaced. This latter condition may result in saturation of certain energy-level pairs and must be considered for accurate linewidth calculations. The linewidth calculations are found to be in very good over-all agreement with experimental values in most cases, although a few discrepancies occur. Comparison of calculated and experimental linewidth data suggest that H20 and SO2 have quadrupole contributions of about 10%-1S% of the observed values while linewidths involving CH 2C12, CH2CF2, and CAO can be explained solely on the basis of dipole-dipole interaction. A value of (2.87±0.10) D. A was determined for the molecular quadrupole moment of N2 from linewidth data for broadening of the 22,0→31,3 transition of H22O by N2 and appears to be in excellent agreement with the value obtained previously from data for NH 3-H2 broadening.